1. Field of the Invention
The present invention relates to a reciprocating compressor and, more particularly, to an apparatus and method for controlling stroke of a reciprocating compressor.
2. Description of the Background Art
In general, a reciprocating compressor sucks and compresses a refrigerant gas by linearly and reciprocally moving a piston in a cylinder and discharges the compressed refrigerant gas. The reciprocating compressor is classified into a recipro type compressor and a linear type compressor according to how the piston is driven.
In the recipro type compressor, a crank shaft is coupled with a rotary motor and a piston is coupled with the crank shaft, so that a rotational force of the rotary motor is changed to reciprocal movement, whereas, in the linear type compressor, a piston connected with an actuator of a linear motor is linearly moved.
Because the linear type reciprocating compressor does not have such a crank shaft which changes rotational movement to linear movement, no frictional loss possibly caused by the crank shaft occurs, and thus, its compression efficiency is high compared with a general compressor.
When the reciprocating compressor is employed in a refrigerator or in an air-conditioner, a voltage applied to a motor of the reciprocating compressor is varied to vary a compression ration of the reciprocating compressor, whereby cooling capacity of the refrigerator or the air-conditioner can be controlled.
An apparatus and method for controlling an operation of the reciprocating compressor in accordance with a conventional art will now be described with reference to FIGS. 1 to 3.
FIG. 1 is a block diagram showing the construction of an apparatus for controlling an operation of a reciprocating compressor in accordance with the conventional art.
As shown in FIG. 1, the conventional apparatus for controlling an operation of a reciprocating compressor includes: a current detecting unit 4 for detecting a current applied to a motor of the reciprocating compressor; a voltage detecting unit 3 for detecting a voltage applied to the motor; a stroke estimator 5 for calculating a stroke estimate value of the reciprocating compressor based on the detected current value, the detected voltage value and parameters (e.g., reactance of the motor, inductance or the motor, a motor constant, etc.) with respect to the motor; a comparator 1 for comparing the calculated stroke estimate value with a pre-set stroke reference value, and outputting a difference signal according to the comparison result value; a controller 2 for controlling a stroke of the reciprocating compressor by varying the voltage applied to the motor; and a power source unit 6 for applying DC power to the current detecting unit 4 and the voltage detecting unit 3.
The operation of the conventional apparatus for controlling an operation of the reciprocating compressor will now be described with reference to FIG. 2.
FIG. 2 is a flow chart of a method for controlling the operation of the reciprocating compressor in accordance with the conventional art.
As shown in FIG. 2, the conventional method for controlling the operation of the reciprocating compressor includes: detecting a voltage and a current applied to a motor of the reciprocating compressor (step S20); calculating a stroke estimate value of the reciprocating compressor based on the detected voltage value, the detected current value and parameters with respect to the motor (step S21); comparing the calculated stroke estimate value with a pre-set stroke reference value (step S22); reducing the voltage applied to the motor if the calculated stroke estimate value is larger than the pre-set stroke reference value (step S23); and increasing the voltage applied to the motor if the calculated stroke estimate value is smaller than the stroke reference value (step S24).
The method for controlling the operation of the reciprocating compressor will now be described in detail.
First, the voltage detecting unit 3 detects a voltage applied to the motor and outputs the detected voltage value to the stroke estimator 5. The current detecting unit 4 detects a current applied to the motor and outputs the detected current value to the stroke estimator 5 (step S20). Herein, in order for the voltage detecting unit 3 to detect a positive voltage and a negative voltage of the AC voltage applied to the motor, a positive DC voltage (e.g., +5V) and a negative DC voltage (e.g., −5V) are to be supplied from the power source unit 6 to a positive voltage supply terminal (+V) and a negative voltage supply terminal (−V) of an OP amplifier of the voltage detecting unit 3. Also, in order for the current detecting unit 4 to detect a positive current and a negative current of the AC current applied to the motor, a positive DC voltage (e.g., +5V) and a negative DC voltage (e.g., −5V) are to be supplied from the power source unit 6 to a positive voltage supply terminal (+V) and a negative voltage supply terminal (−V) of an operational (OP) amplifier of the current detecting unit 4.
The stroke estimator 5 calculates the stroke estimate value by applying the detected current value, the detected voltage value and parameters of the motor to equation (1) shown below, and outputs the calculated stroke estimate value to the comparator 1 (step S21):
                    x        =                              1            a                    ⁢                      ∫                                          (                                                      V                    M                                    -                                      R                    ⁢                                                                                  ⁢                    i                                    -                                      L                    ⁢                                                                                  ⁢                                          i                      _                                                                      )                            ⁢                              ⅆ                t                                                                        (        1        )            wherein ‘R’ is resistance of the motor, ‘L’ is inductance of the motor, a is a motor constant, VM is a voltage value applied to the motor of the reciprocating compressor, and ‘i’ is a current value applied to the motor.
Thereafter, the comparator 1 compares the calculated stroke estimate value with the pre-set stroke reference value, generates a difference signal according to the comparison result value, and outputs the generated difference signal to the controller 2 (step S22).
The controller controls the stroke of the reciprocating compressor by varying the voltage applied to the motor based on the difference signal. Namely, if the calculated stroke estimate value is larger than the pre-set stroke reference value, the controller 2 reduces the voltage applied to the motor (step S23), whereas if the calculated stroke estimate value is smaller than the pre-set stroke reference value, the controller 2 increases the voltage applied to the motor (step S24).
That is, the conventional apparatus for controlling the operation of the reciprocating compressor controls the stroke of the reciprocating compressor by detecting the voltage and current applied to the motor and calculating the stroke estimate value of the reciprocating compressor based on the detected voltage and the detected current.
The power source unit 6 applies DC power to the voltage detecting unit 3 and the current detecting unit 4 so that the voltage detecting unit 3 and the current detecting unit 4 can detect the voltage and the current, respectively. Namely, the power source unit 6 applies DC voltages (e.g., +5V and −5V) to the positive voltage supply terminal (+V) and the negative voltage supply terminal (−V) of the OP amplifiers of the voltage detecting unit 3 and the current detecting unit 4, respectively, so that the voltage detecting unit 3 can detect the positive and negative voltages applied to the motor and the current detecting unit 4 can detect the positive and negative currents passing through the motor.
FIG. 3 shows the power source unit of the apparatus for controlling the operation of the reciprocating compressor in accordance with the present invention.
As shown in FIG. 3, in order to supply DC voltages (e.g., +5V and −5V) to the voltage detecting unit 3 and the current detecting unit 4, the power source unit 6 includes a positive voltage regulator L7805 and a negative voltage regulator UA7905.
However, the conventional apparatus for controlling the operation of the reciprocating compressor is disadvantages in that since it uses the elements for detecting all the positive and negative voltages of the AC voltage applied to the motor of the reciprocating compressor and the positive and negative currents of the AC current passing through the motor, costs for implementing the reciprocating compressor and its power consumption increase.